Changes in cranberry phenology from 1958 to 2022: Implications for spring frost protection in Massachusetts, United States.

Abstract

Warmer temperatures associated with climate change have affected the phenology of most plants, but limited information exists for the American cranberry (Vaccinium macrocarpon Ait.), an important specialty crop. We examined long-term spatiotemporal trends in spring development of cranberry buds using field observations of cranberry bud stages over a 65-yr period, spanning from 1958-2022. A growing degree day (GDD) model was further used to interpret the observed trends in bud development over the study period. To assess spatial variability in cranberry bud development, the GDDs were computed using gridded weather data for four counties of Massachusetts, representing 85% of the state's cranberry acreage. A Theil-Sen linear regression model was implemented to determine trends in the occurrence of the bud stages. Field observations revealed significant temporal trends (p-value < 0.01) in the annual timing of white bud and cabbage head stages, occurring 18-20 days earlier in the spring than 65 years ago. This earlier bud development can increase the risk of frost damage, especially during late-spring freezes. GDDs accumulated at a faster rate towards the end of the study period due to rising air temperatures. Analysis of 65 years of gridded data revealed a significant trend of earlier development across the four counties. The rate of advancement in cabbage head stage ranged from -0.15 to -0.25 d yr ^-1 across the study area. These findings highlight the need for updated frost forecasting models that account for the changing growth schedule of cranberry.